MORPHOLOGY AND TAXONOMY OF MASTIGOPHORA 269 



the groove approaches the anterior end and finally disappears 

 entirely from the cell. In Prorocentnim (Fig. 129, A) there is an 

 anterior spur-like process about which the transverse flagellum 

 vibrates as though in a groove, while in Exuimlla even this spur is 

 absent but the flagellum vibrates in a plane at right angles to the 



Fig. 129. — Types of Diiioflagellida. A, Prorocentrum micans; B, ExuviwUa 

 marina; C, Gyrodinium ovum; D, Gyinnodinium sphcericum; E, Pcridinium divergens. 

 (A, after Blitschli; B, to E after Calkins.) 



long axis of the cell as though in an imaginary furrow (Fig. 129, B). 

 It seems highly improbable that such a peculiar mode of flagellar 

 vibration is evidence of a primitive form of Dinoflagellates and more 

 reasonable to regard these types as secondarily simplified organisms 

 derived from the Dinophysidse, a derivation further evidenced by 



